Field of the Invention
The present invention relates to an identification film and pattern including photonic crystals and an anticounterfeiting product including the same and more particularly to an identification film and pattern having high transparency and reflectance spectra with respect to particular wavelengths and including photonic crystals patterned into a particular shape and an anticounterfeiting product including the same.
Description of the Related Art
Photonic crystals are materials with photonic bandgaps by periodic changes in dielectric constant at half the wavelength of light. In this regard, photons with energy corresponding to photonic bandgaps cannot propagate into photonic crystals due to very low state density of photonic crystals and, when a photonic bandgap is present in a visible light region, this immediately appears a reflection color.
Regular arrays of colloidal particles exhibit a reflection color by the same principle and the reflection color corresponds to the bandgap of photonic crystals. The reflection color of colloidal photonic crystals is determined by indexes of refraction, crystal structures, particle sizes, interparticle spaces and the like of colloids and the surrounding materials. Thus, photonic crystals with a desired reflection color may be prepared by controlling these properties.
Film-type photonic crystals are mainly formed by vertical coating and spin-coating. Vertical coating may be used to prepare a thick film having high reflectance (P. Jiang, J. F. Bertone, K. S. Hwang, and V. L. Colvin, “Single-Crystal Colloidal Multilayers of Controlled Thickness”, Chemistry of Materials, 11, 2132-2140 (1999)). However, the prepared thick film has very weak mechanical strength in terms of structure and is easy to break and is prepared by an evaporation process, which results in increased manufacturing time. In addition, there are many cracks in colloidal crystals prepared by vertical coating and thus it is difficult to practically apply such colloidal crystals.
In spin coating (Journal of American Chemical Society, 126, 13778-13786 (2006); U.S. Patent Publication No.: 2005/0095471), crystals may be rapidly prepared, but it is difficult to prepare thick crystals with high reflectance and to adjust lattice constant and thus it is difficult to realize various reflection colors using particles having the same size, and it is difficult to re-coat another material with such crystals after production due to large crystal size.
To address the above-described problems, the inventors of the present invention proposed a paint composition pigment including photonic crystals having high reflectance and showing various reflection colors and a method of preparing the same, disclosed in Korean Patent Publication No.: 10-2010-40527. The patent application discloses a method of preparing a film by dispersing colloids in a monomer resin and photo-curing the resultant material. However, there is still a need to develop a technology for applying the paint composition to a variety of fields. For example, there is a need to develop a method of further enhancing identification capability, security, convenience in terms of use, and the like of the paint composition of the disclosed patent.